.app {
  height: 100%;
  width: 100%;
  display: flex;
  flex-direction: column;
  & > header {
    min-height: 50px;
    background-color: aqua;
  }
  & > footer {
    min-height: 50px;
    background-color: aqua;
  }
  & > main {
    flex: 1 1 auto; 
    display: flex;
    & > .ant-menu {
      width: 200px;
    }
    & > .content {
      flex: 1 1 auto; 
      position: relative;
    }
  }
}